This is a remote forest in Western Poland, where 400 pine trees have grown with a curvature in their trunk structure and it turns out that no one really knows exactly what caused it. There are, however, a few theories:

1) The main theory seems to suggest that this is the result of human interference. It is believed that this is a tree farm and the trees were forced to grow horizontally in their youth to make a carpenters life easier. The curved shape can be induced by laying a heavy object over a young tree stem. Phototropism will cause the stem beyond the heavy object to grow toward the sky, while the growing stem beneath and behind the heavy object will develop what is called morphogenetic compression wood - which ultimately makes the curve in the stem permanent.

The problem with this theory is there is no evidence of a carpenter nearby and as the trees are relatively young (90 years) you would think someone would local would have some insight.

2) The other theory suggests that the curved formation is simply a result of heavy snow load combined with a long spring melt. The trees become photosynthentically active as the angle of the sun increases during spring. With a snow load still on the stem during this period, compression wood forms as the trees grow; resulting in a permanent bend.

Again, another problem comes from this theory; why did snow effect just these 400 trees, rather than the whole pine forest?

3) A third expalnation could be soil creep; as colder temperatures pervade the area, the moisture in the soil freezes and expands, displacing the soil and anything not held fast in it (ie. saplings), then during the warmer part of the day, thaws and retracts. Over days, tiny saplings can be moved to angles ranging from just slightly off 90° to laying flat against the ground as if they had fallen. The saplings prefer very much to remain vertical, as their ability to be able to catch sunlight to keep photosynthesizing is dependent on it, so it will actually bend itself towards the sunlight, much like a sunflower turning its 'head' to face the sun. The result, these curved trunks of trees until they are old enough to grow straight up, and not be affected by soil creep. This phenomenon is most prevalent on hilly terrain, as the steepness of the slope causes for more drastic soil creep.

Once again; this theory falls short; the area is not particularly hilly, especially not to the extent of causing such a dramatic curvature.